"Dr John H. Watson M.D." was the literary alias of the assistant to the detective Sherlock Holmes. According to some accounts he was a real person with the first name of "James" who inspired a literary character. (PROSE: Prelude All-Consuming Fire) Others held that Sherlock Holmes, and therefore he himself, were entirely fictional. (TV: The Snowmen)

On both occasions of their meeting the Doctor and his associates (and during the various references to said meetings) it is suggested that Sherlock Holmes and John Watson are not in fact their real names, but the pseudonyms used in the fictional stories written about them. Information regarding their encounters with Bernice Summerfield and Ace is only provided in subjective form by Bernice herself and Watson, each of whom maintained diaries of said events. (PROSE: All-Consuming Fire, Happy Endings)

The television story The Snowmen suggested that stories of Holmes and Watson were inspired by the adventures of Madame Vastra and Jenny Flint, which might imply that Jenny was the "real" John Watson within the context of the Doctor Who universe. The reference book Doctor Who: The Secret Lives of Monsters includes an excerpt from a book called A Study in Green in which Vastra, Jenny and Strax encounter Holmes and Watson. Jenny bought all 200 copies of the book to keep it off the shelves.